Certain structural members in buildings are subject to, and required to resist, various forces.
For example, in portal frames, which are commonly used in building construction, an inclined rafter may extend between a substantially vertical column and an apex of the portal frame and may in use be required to resist forces resulting from, for example, the weight of parts of the building, wind loads, additional forces such as those resulting from a person walking on the roof of the building, and other forces.
In a known portal frame, the material and dimensions of the rafters are selected to allow the rafters, each of which is of substantially uniform in transverse cross sectional shape and size along its length, to adequately resist the forces to which they are expected to be subject and which they are required to resist in use.